1. Field of the Invention
Aspects of the present invention relate to a cylindrical secondary battery, and more particularly, to a cylindrical secondary battery including a gasket that improves the coupling of a cap up and a safety vent.
2. Description of the Related Art
Generally, a secondary battery can be classified as cylindrical, rectangular, or pouch-type, according to a shape of a case of the battery.
In a cylindrical secondary battery, an electrode assembly is inserted into a cylindrical can, and then a cap assembly is assembled to an upper opening of the cylindrical can. The cap assembly is electrically coupled to the electrode assembly, to transmit current to an external device.
The cap assembly improves the stability of the battery, by reducing an internal pressure of the can, or by interrupting current flow. The internal pressure can be increased by overcharging, or an abnormal operation of, the battery, which can cause an explosion.
The cap assembly includes a cap up (cathode terminal), and a safety vent that is provided under the cap up. The safety vent is deformed to interrupt current, or to discharge gas to relieve the increased internal pressure. A cap down and a sub-plate are sequentially provided under the safety vent, and are connected to a cathode of the electrode assembly.
Vibrations or external impacts applied to a cylindrical battery can result in an unwanted increase in the resistance of contact surfaces between components of the cap assembly. Particularly, battery performance is degraded, when the contact resistance, of an interfacial surface between the safety vent and cap up, is increased.
To solve the above problem, the contact surfaces of the safety vent and cap up can be welded, or the safety vent can be bent, to surround an outer surface of the cap up. However, the welding complicates an assembling process of a battery, and defects can occur, when the welding is not properly performed.
In addition, it is difficult to bend the safety vent, so as to surround the outer circumference surface of the cap up, because thickness of the cap up is increased in high-capacity secondary batteries. In addition, in high capacity secondary batteries, the pressing force of a gasket is reduced, because of the larger thickness of the stacked portions of the cap up and the safety vent.